Conventionally is known a rear chassis system in which rear wheel suspension assemblies are mounted on the vehicle body via a subframe. (Refer to Japanese patent laid open (kokai) publication No. 5-8643.) According to this conventional system, a fuel tank is supported by the subframe which is in turn mounted on the vehicle body. Therefore, a step of mounting the fuel tank on the subframe needs to be carried out before mounting the subframe on the vehicle body, and this may increase the complexity of the assembling process.
Additionally, interference between the subframe members and the fuel tank must be avoided, and it creates some difficulty in ensuring the necessary capacity of the fuel tank, and the necessary mechanical strength and rigidity of the subframe with the result that the weight of the rear chassis and the manufacturing cost tend to be increased.